The light-emitting diode (LED) is a solid state semiconductor device, which has been broadly used as a light-emitting device. The light-emitting device structure at least comprises a p-type semiconductor layer, an n-type semiconductor layer, and an active layer. The active layer is formed between the p-type semiconductor layer and the n-type semiconductor layer. The structure of the light-emitting device generally comprises III-V group compound semiconductor such as gallium phosphide, gallium arsenide, or gallium nitride. The light-emitting principle of the LED is the transformation of electrical energy to optical energy by applying electrical current to the p-n junction to generate electrons and holes. Then, the LED emits light when the electrons and the holes combine.
FIG. 1 illustrates a cross-sectional diagram of a conventional light-emitting device before bonding process. The light-emitting device comprises a semiconductor layer sequence 10a provided with a first main side 18 and a second main side 181, comprising a first semiconductor layer 11, a second semiconductor layer 13, and an active layer 12 formed between the first semiconductor layer 11 and the second semiconductor layer 13, which can produce electromagnetic radiation. A trench is formed in the semiconductor layer sequence 10a by wet etch or dry etch. A dielectric layer 14 is formed on the inner sidewall of the trench to electrically insulate the second semiconductor layer 13 and the active layer 12. Then, an electrically conductive material is filled into the insulated trench, so a first metal layer 15 is formed. A reflecting layer 16 is formed between the semiconductor layer sequence 10a and the dielectric layer 14. A void 17 is an area not occupied by the first metal layer 15. A first connection layer 101 formed on a carrier substrate 102 is used to connect the first metal layer 15. The first connection layer 101 and the first metal layer 15 are connected together in an electrically conductive manner. As shown in FIG. 1, after forming the first connection layer 101 and the first metal layer 15, the semiconductor layer sequence 10a is connected to the carrier substrate 102 by metal bonding or glue bonding.
FIG. 2A illustrates a cross-sectional diagram of a conventional light-emitting device 20. As shown in FIG. 2A, connecting failure problem arises in the bonding process. FIG. 2A shows the result of the bonding process after a first metal layer 25 is connected to a first connection layer 201. However, because the trench is deep, it is not easy to fill the trench with electrically conductive material, and the profile of the trench is concave after the filling process. While the first metal layer 25 is connected to the first connection layer 201 of a carrier substrate 202, a void 204 is formed between the first metal layer 25 and the first connection layer 201. Thus, the connection area between the first metal layer 25 and the first connection layer 201 is small and the resistance of the light-emitting device 20 is therefore raised. As shown in FIG. 2B, the peripheral area of the trench 200 is occupied by the first metal layer 25, and the internal area not occupied by the first metal layer 25 forms the void 204.